The generator stator core is the largest monobloc component in the train of a turbine generator set. The stator cores are manufactured from thousands of thin steel laminations of which are stacked, pressed and clamped together into the large cylindrical form of the stator core. The clamping is necessary for several reasons but principally to ensure that geometric form is maintained under the forces imposed during unit operation. Improper clamping can result in lamination vibration during generator operation, due to magnetic impulses and/or core elliptical dilation.
Typically, the stator core is assembled at the final installation site. However, the large size of the stator core and the need for proper clamping results in several stator core manufacturing complexities, including the need for generous floor space, high crane requirements, lead time and other associated manufacturing difficulties. For example, if the core is stacked directly in the stator frame, the frame must be delivered to the site before any manufacturing steps can occur. Additionally, intermediate core pressing equipment is needed to press and clamp the laminations together at incremental lengths. If, on the other hand, the stator core is manufactured in an external fixture, the external fixture itself adds to the manufacturing costs and requires additional floor space on site and still requires the use of heavy cranes.
U.S. Pat. No. 5,875,540 by Sargeant, which is incorporated herein by reference, overcame some of the problems with the prior art by first assembling a number of laminations into a distinct set, referred to as a donut, and then stacking these donuts to form a stator core. This saved great amounts of time over assembling the laminations individually, and produced a stator core with less flaws.
When the individual laminations, or the set of laminations in a donut, are installed into a core, they engage what are referred to as keybars. Keybars are essentially rods that run the internal length of the stator core and provide a hook-in spot for the laminations. FIG. 1 illustrates a stator frame that is empty of any laminations. The keybars 6 run the internal length of the stator frame 2, and are generally attached to the frame through stator support rings 4.
The laminations have complimentary grooves that hook onto the keybars, as shown in FIG. 2. In this figure, a typical styles of keybars and grooves are shown. FIG. 2 illustrates the dovetail design, where the lamination 10 has a groove 12 that matches the keybar 6. By sliding the lamination 10 onto the keybars 6, the laminations are held in place within the stator frame. Since the stator core will vibrate during operation, it is important that the keybars and any attachment to the keybars, are held tightly against the core.
Since the laminations may be mounted individually or in aggregates such as donuts, if the fit between the lamination grooves 12 and the keybars 6 is too tight, installation can be very difficult or, in the extreme, precluded. Thus, there is a need for laminations or donuts that are easily placed onto keybars, but are still able to be tightly fitted.